Ubiquitous real-time fracture monitoring

ABSTRACT

Method for characterizing subterranean formation is described. One method involves simulating a poroelastic pressure response of known fracture geometry utilizing a geomechanical model to generate a simulated poroelastic pressure response. Compiling a database of simulated poroelastic pressure responses. Measuring a poroelastic pressure response of the subterranean formation during a hydraulic fracturing operation to generate a measured poroelastic pressure response. Identifying a closest simulated poroelastic pressure response in the library of simulated poroelastic pressure response. Estimating a geometrical parameter of a fracture or fractures in the subterranean formation based on the closest simulated poroelastic pressure response.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application which claims benefitunder 35 USC § 119(e) to U.S. Provisional Application Ser. No.62/669,065 filed May 9, 2018, entitled “Ubiquitous Real-Time FractureMonitoring,” which is incorporated herein in its entirety.

The present invention is related to similar subject matter of co-pendingand commonly assigned U.S. patent application entitled “Measurement ofPoroelastic Pressure Response” filed on May 9, 2018, which is herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to recovery of hydrocarbons fromunconventional reservoirs. More particularly, but not by way oflimitation, embodiments of the present invention include tools andmethods for real-time monitoring of hydraulic fracture geometry byquickly interrogating and finding a match in a database of poroelasticpressure signatures.

BACKGROUND OF THE INVENTION

During hydraulic fracturing stimulation process, highly pressurizedfluids are injected into a reservoir rock. Fractures are created whenthe pressurized fluids overcome breaking strength of the rock (i.e.,fluid pressure exceeds in-situ stress). These induced fractures andfracture systems (network of fractures) can act as pathways throughwhich oil and natural gas migrate en route to a borehole and eventuallybrought up to surface. Efficiently and accurately characterizing createdfracture systems is important for optimizing hydraulic fracturing.Determination and evaluation of hydraulic fracture geometry caninfluence field development practices in a number of important ways suchas, but not limited to, well spacing/placement design, infill welldrilling and timing, and completion design.

More recently, fracturing of shale from horizontal wells to produce gashas become increasingly important. Horizontal wellbore may be formed toreach desired regions of a formation not readily accessible. Whenhydraulically fracturing horizontal wells, multiple stages (in somecases dozens of stages) of fracturing can occur in a single well. Thesefracture stages are implemented in a single well bore to increaseproduction levels and provide effective drainage. In many cases, therecan also be multiple wells per location.

There are several conventional techniques (e.g., microseismic imaging)for characterizing geometry, location, and complexity of hydraulicfractures. As an indirect method, microseismic imaging technique cansuffer from a number of issues which limit its effectiveness. Whilemicroseismic imaging can capture shear failure of natural fracturesactivated during well stimulation, it is typically less effective atcapturing tensile opening of hydraulic fractures itself. Moreover, thereis considerable debate on interpretations of microseismic events as itrelates to hydraulic fractures.

While our understanding of what hydraulic fractures look like in shalereservoirs has improved, data acquisition for most wells tend to belimited with little to no information for characterizing stimulatedreservoir volume (SRV). Hence, completion and reservoir engineers areoften left to rely on production performance over several months/yearsto optimize field design and evaluate effectiveness of a completiondesign. Thus, one of the key challenges in hydraulic fracturing isaccelerating this learning process to improve well performance andrecovery.

BRIEF SUMMARY OF THE DISCLOSURE

The present invention relates generally to recovery of hydrocarbons fromunconventional reservoirs. More particularly, but not by way oflimitation, embodiments of the present invention include tools andmethods for real-time monitoring of hydraulic fracture geometry bycharacterizing main characteristics of poroelastic responses measuredduring hydraulic stimulation and quickly interrogating and finding amatch in database of poroelastic pressure signatures.

The present invention can monitor evolution of reservoir stressesthroughout lifetime of a field during hydraulic fracturing. Measuringand/or identifying favorable stress regimes can help maximize efficiencyof multi-stage fracture treatments in shale plays.

One example of a method for characterizing a subterranean formationincludes: a) simulating a poroelastic pressure response of knownfracture geometry utilizing a geomechanical model to generate asimulated poroelastic pressure response; b) repeating a) to compile adatabase of simulated poroelastic pressure responses; c) measuring aporoelastic pressure response of the subterranean formation during ahydraulic fracturing operation to generate a measured poroelasticpressure response; d) identifying a closest simulated poroelasticpressure response in the library of simulated poroelastic pressureresponse; and e) estimating a geometrical parameter of a fracture orfractures in the subterranean formation based on the closest simulatedporoelastic pressure response.

Another example of a method for characterizing a subterranean formationincludes: a) compiling a database of simulated poroelastic pressureresponses of stimulated fractures, wherein the library is stored in anon-transitory computer storage medium; b) obtaining a poroelasticpressure response of the subterranean formation during a hydraulicfracturing operation to generate a measured poroelastic pressureresponse; c) using a computer-processor to query the database ofsimulated poroelastic pressure responses to identify a closest simulatedporoelastic pressure response; and d) estimating a geometrical parameterof a fracture or fractures in the subterranean formation based on theclosest simulated poroelastic pressure response.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and benefitsthereof may be acquired by referring to the follow description taken inconjunction with the accompanying drawings in which:

FIGS. 1A-1B illustrates poroelastic behavior in high permeability (FIG.1A) and low permeability (FIG. 1B) systems.

FIGS. 2A-2B illustrate a set simulated poroelastic pressure responsecurves of a known fracture geometry and observation points.

FIG. 3 illustrates an example of multiple well configuration duringhydraulic fracturing.

FIGS. 4A-4D illustrates downhole monitor vertical well configurationssuitable for measuring poroelastic pressure response according to one ormore embodiments.

FIG. 5 illustrates downhole well configuration suitable for measuringporoelastic pressure response in which the pressure gauge is installedoutside of the casing according to one or more embodiments.

FIGS. 6A-6C illustrate horizontal well configurations suitable formeasuring poroelastic pressure response according to one or moreembodiments.

FIG. 7 illustrates a workflow for one or more embodiments of the presentinvention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the invention,one or more examples of which are illustrated in the accompanyingdrawings. Each example is provided by way of explanation of theinvention, not as a limitation of the invention. It will be apparent tothose skilled in the art that various modifications and variations canbe made in the present invention without departing from the scope orspirit of the invention. For instance, features illustrated or describedas part of one embodiment can be used on another embodiment to yield astill further embodiment. Thus, it is intended that the presentinvention cover such modifications and variations that come within thescope of the invention.

The present invention relates generally to recovery of hydrocarbons fromunconventional reservoirs. More particularly, but not by way oflimitation, embodiments of the present invention include tools andmethods for real-time monitoring of hydraulic fracture geometry byquickly interrogating and finding a match in a database of poroelasticpressure signatures.

One of the goals of this technology is to enable cost effectivecharacterization of the induced fracture system on virtually every wellwith little to no impact on ongoing operations. It has the potential tobe used universally during fracturing operations in shale wells.

There are several advantages to the proposed invention. First is anability to leverage knowledge from field pilots, instrumented wells andextend it to majority of wells for which there is limited data.Interpretations based on pressure data such as poroelastic responsemonitoring can be calibrated during pilot tests using number of methodsincluding, but not limited to, distributed acoustic/temperature sensing(DAS/DTS), microseismic or tiltmeter monitoring, tracers, and then beapplied in non-instrumented wells.

Another advantage capitalizes on the resulting quick speed of pressuredata interpretation. For example, by training a neural network usingsynthetic cases of numerically-generated pressure response (for whichinduced-fracture characteristics are known), the present invention canquickly relate the measured poroelastic pressure response to fracturegeometries and generate a real-time map. Other advantages will beapparent from the disclosure herein.

Poroelastic Pressure Response

During hydraulic stimulation, pressure data at active and offset wells(in multi-well pads) is easily available. However, this data istypically under-utilized. When correctly understood, this data reflectsmany physical phenomena beyond just momentum diffusion and includestremendous information about the created SRV. At offset wells, manypressure changes can be seen during hydraulic fracturing operations. Itis now known that many of them are poroelastic pressure responses whereno fluid communication is being established between the active andoffset wells. Instead, pressure changes are due to stresses imposed bydilated fractures (“squeezing” effect). These tensile dilations canalter reservoir stresses up to thousands of feet away from the fracturesthus “squeezing” the surrounding rock. In high permeability systems, afluid will be open to mass transfer so that pore pressure stays constant(FIG. 1A).

In low permeability systems (such as shale), the rock is closed to fluidmass transfer which causes the pore pressure to increase (FIG. 1B). Onecan measure the resulting poroelastic pressure response which can alsobe defined as a pressure change in the subsurface resulting from achange in volumetric stresses. A change in volumetric stress can berelated back to a geomechanical phenomena. In other words, theporoelastic pressure response is a pressure signature that is notrelated to flow or hydraulic communication with the stimulated well butis a proxy for mechanical deformation and/or stress interference. Anin-depth description of poroelastic pressure response and its use tocharacterize fractures is described in U.S. Publication US20150176394,the contents of which are hereby incorporated by reference.

FIG. 2B shows a set of numerically simulated poroelastic pressureresponse curves to fracture propagation and closure, at multiplelocations in the reservoir. FIG. 2A illustrate the hydraulic fractureand observation points corresponding to the curves. The fracturedimensions at the end of propagation are 775 ft (half-length) by 160 ft(height). As the fracture tip approaches the observation point, adecrease in pressure is observed resulting from tensile stresses. As thefracture continues to propagate, we see that the squeezing effect willproduce an increase in pressure along observation points (150 ft, 300ft, 450 ft, 600 ft, 750 ft from where the fracture initiates). After thewell is shut-in at the end of the fracturing stage, poroelastic pressuredeclines due to leak-off and closure of the hydraulic fracture.

Downhole Configurations for Measuring Poroelastic Pressure Response

FIG. 3 illustrates a common hydraulic fracturing setup that includes anactive/stimulated well, offset well, and monitor well. As shown, apressure gauge can be installed at the surface in the offset well and/ormonitor well (not shown). The downhole well configurations of FIGS.4A-4D, FIG. 5, and FIG. 6 can be viewed within the context of FIG. 3.

FIGS. 4A-4D illustrate different vertical well configurations that allowmeasurement of poroelastic pressure response through or in a monitorwell. In these scenarios, the hydraulic fractures were generated in anearby active well. FIG. 4A shows a single zone configuration of aperforated monitor well (unstimulated). As shown, a pressure gauge canbe installed at the surface to measure poroelastic pressure responsethrough the perforations. FIG. 4B shows a multi-zone configuration of aperforated monitor well (unstimulated). As shown, each zone has beensealed with a solid plug. This allows pressure gauges to be installed atvarious locations (e.g., surface, downhole within each zone, etc.) andlocally measure poroelastic pressure response. FIG. 4C shows a singlezone configuration of a stimulated monitor well. FIG. 4D shows amulti-zone configuration of a stimulated monitor well. In both of theseconfigurations the poroelastic pressure response is measured through themonitor well's hydraulic fractures and perforations.

FIG. 5 illustrates another vertical well measurement configuration. Herethe pressure gauge is installed outside of the casing and can measureporoelastic pressure response through the porous rock formation.

FIG. 6A-6C illustrate different horizontal well configurations. FIG. 6Ashows pressure gauges installed outside of the casing at multiplereservoir locations. FIG. 6B shows poroelastic pressure measurementstaken at the surface through the toe prep. FIG. 6C shows how pressuremeasurement can be taken at the surface through a fracture stage.

Utilizing Poroelastic Pressure Response in Real-Time

The present invention automates processing of active/offset wellporoelastic pressure data by extracting its essential characteristics(e.g., time-lag, magnitude, slope) and accelerating its interpretationto provide a real-time interpreted map of each fracturing stage. Theinterpretations can include estimates of physical characteristics suchas length, height, orientation, fracture asymmetry, residual width fromproppant, and the like. These estimates can be based on a database orlibrary of previously studied poroelastic pressure response (“pressuresignatures”). In some embodiments, the database will include asearchable library of simulated or modeled pressure signatures (e.g.,FIG. 2). In some embodiments, the database may include full or partialpressure signatures. In some embodiments, the database also includespressure signatures obtained from field data (e.g, microseismicmonitoring, distributed acoustic/temperature sensing, tiltmetermonitoring, fluid and proppant tracers, production logs, etc.). A usercan query the database based on any one or combination of the essentialcharacteristics (i.e., time-lag, magnitude, slope, etc.) to find amatch. The process is analogous to finding a fingerprint match whereseveral key features of the measured poroelastic pressure response iscompared against a database of poroelastic pressure responses to find amatch.

Combining the automated processing of acquired poroelastic pressure datawith corresponding completion design characteristics allows optimizationof completion design by means of machine learning techniques. Low-costnature of the data and negligible impact on field operations means thistechnology may be applied on virtually all multi-pad wells. With theassistance of data analysis techniques, poroelastic pressure data may beprocessed in real time to provide an immediate assessment of the SRV,thus enabling decisions “on the fly” and even testing of severalcompletion designs on a single well or pad.

Thus, the present invention provides a quick feedback mechanism forunderstanding geometry of induced fractures and its relationship tocompletion designs. This allows engineers to make changes to fracturingdesign (e.g., rate, proppant concentration, volume) on the fly andoptimize completion in real time. Affordable, real-time, systematicfracture monitoring enabled by physics-informed data analytics and/ormachine learning would considerably reduce learning time and allowfaster convergence to optimum development scenarios.

According to one or more embodiments, FIG. 7 illustrates a real-timeworkflow of fracture mapping and completion optimization based oninterpretation of poroelastic pressure responses during hydraulicstimulation of a field. Referring to FIG. 7, the first step of theworkflow involves extracting essential characteristics of the reservoiror field from the acquired poroelastic pressure responses (pressureversus time). These essential characteristics can be obtained bymeasuring the poroelastic pressure response after stimulation has begun.Some of these characteristics include elapsed time to reach maximumpressure (Δt_(max)), elapsed time to reach minimum pressure (Δt_(min)),maximum deviation in poroelastic pressure (Δp_(max)), minimum deviationin poroelastic pressure (Δp_(min)), and maximum slope (max Δp/Δt).

The poroelastic response database can include results from numericalsimulations of poroelastic response of known fracture dimension,interpretation of prior field poroelastic responses, and other fieldfracture diagnostic data. The database can be queried using any of theessential characteristics, fracture dimension or dimensions, or even theshape of the poroelastic response curve. Integration of the poroelasticresponse database with machine learning capabilities (e.g., neuralnetworks) can improve accuracy of fracture dimension predictions.

Once a match has been identified, dimensions (length, height, width,orientation, etc.) of the stimulated fractures can be estimated.Moreover, the database can be augmented or tagged with additionalparameters such as best completion design parameters (injection rate,fluid type/volume, proppant type/volume, cluster/stage spacing, etc.)and geological parameters (landing depth, mechanical properties, etc.)and well performance.

With this information in hand, a completion engineer can query thedatabase to obtain not only fracture dimensions but suggested completionparameters while considering factors such as geological parameters andwell performance. Thus, the completion design is improved in real-time.

Although the systems and processes described herein have been describedin detail, it should be understood that various changes, substitutions,and alterations can be made without departing from the spirit and scopeof the invention as defined by the following claims. Those skilled inthe art may be able to study the preferred embodiments and identifyother ways to practice the invention that are not exactly as describedherein. It is the intent of the inventors that variations andequivalents of the invention are within the scope of the claims whilethe description, abstract and drawings are not to be used to limit thescope of the invention. The invention is specifically intended to be asbroad as the claims below and their equivalents.

The invention claimed is:
 1. A method for characterizing a subterraneanformation comprising: a) simulating a poroelastic pressure response ofknown fracture geometry utilizing a geomechanical model to generate asimulated poroelastic pressure response; b) repeating a) to compile adatabase of simulated poroelastic pressure responses; c) measuring aporoelastic pressure response of the subterranean formation during ahydraulic fracturing operation to generate a measured poroelasticpressure response; d) identifying from the measured poroelastic pressureresponse a closest simulated poroelastic pressure response in thelibrary of simulated poroelastic pressure responses; and e) estimating ageometrical parameter of a fracture or fractures in the subterraneanformation based on the closest simulated poroelastic pressure response.2. The method of claim 1, wherein the geometrical parameter is one ormore of: height of fracture, length of fracture, width of fracture,fracture asymmetry, residual width from proppant, orientation offracture, stimulated reservoir volume, and drained reservoir volume. 3.The method of claim 1, wherein the database of simulated poroelasticpressure responses is searchable by one or more of: elapsed time toreach maximum pressure, elapsed time to reach minimum pressure, maximumdeviation in poroelastic pressure, minimum deviation in poroelasticpressure, and maximum slope.
 4. The method of claim 1, wherein theestimating of dimension or dimensions of a fracture or fractures iscompleted in real-time as the hydraulic fracturing operation isperformed.
 5. The method of claim 1, wherein the hydraulic fracturingoperation is a multi-stage hydraulic fracturing operation.
 6. The methodof claim 1, further comprising: f) selecting a completion designparameter of the subterranean formation in real-time.
 7. The method ofclaim 6, wherein the completion design parameter is one or more of: rateof subterranean fluid introduced, proppant concentration, proppantvolume, and injection rate.
 8. The method of claim 1, wherein theporoelastic pressure response is measured at surface or in a well. 9.The method of claim 1, wherein the database of simulated poroelasticpressure responses includes at least one suggested completion designparameter selected from: injection rate, fluid type, fluid volume,proppant type, proppant volume, cluster spacing, and stage spacing. 10.The method of claim 1, wherein the database of simulated poroelasticpressure responses includes field data, completion design parameter, orwell performance data.
 11. A method for characterizing a subterraneanformation comprising: a) compiling a database of simulated poroelasticpressure responses of stimulated fractures, wherein the library isstored in a non-transitory computer storage medium; b) obtaining aporoelastic pressure response of the subterranean formation during ahydraulic fracturing operation to generate a measured poroelasticpressure response; c) using a computer-processor to query the databaseof simulated poroelastic pressure responses to identify a closestsimulated poroelastic pressure response based on the measuredporoelastic pressure response; and d) estimating a geometrical parameterof a fracture or fractures in the subterranean formation based on theclosest simulated poroelastic pressure response.
 12. The method of claim11, wherein the geometrical parameter is one or more of: height offracture, length of fracture, width of fracture, fracture asymmetry,residual width from proppant, orientation of fracture, stimulatedreservoir volume, and drained reservoir volume.
 13. The method of claim11, wherein the database of simulated poroelastic pressure responses issearchable by one or more of: elapsed time to reach maximum pressure,elapsed time to reach minimum pressure, maximum deviation in poroelasticpressure, minimum deviation in poroelastic pressure, and maximum slope.14. The method of claim 11, wherein the estimating of dimension ordimensions of a fracture or fractures is completed in real-time as thehydraulic fracturing operation is performed.
 15. The method of claim 11,wherein the hydraulic fracturing operation is a multi-stage hydraulicfracturing operation.
 16. The method of claim 11, further comprising: e)selecting a completion design parameter of the subterranean formation inreal-time.
 17. The method of claim 16, wherein the completion designparameter is one or more of: rate of subterranean fluid introduced,proppant concentration, proppant volume, and injection rate.
 18. Themethod of claim 11, wherein the poroelastic pressure response ismeasured at surface or in a well.
 19. The method of claim 11, whereinthe database of simulated poroelastic pressure responses includes atleast one suggested completion design parameter selected from: injectionrate, fluid type, fluid volume, proppant type, proppant volume, clusterspacing, and stage spacing.
 20. The method of claim 11, wherein thedatabase of simulated poroelastic pressure responses includes a fielddata, completion design parameter, or well performance data.